High-tensile steel with excellent weldability and toughness and with tensile strength of 550 MPa class or more and method of production of the same

摘要

The present invention provides a high-tensile steel material having a tensile strength of the 550 MPa class or more which can simultaneously raise the strength and toughness of the heat affected zone of weld to equal those of the matrix and a method of production of the same, that is, a high-tensile steel material with excellent weldability and toughness and with tensile strength of the 550 MPa class or more containing, by mass %, C: 0.005 to 0.10%, W: 0.10 to 3.0%, Nb: 0.010 to 0.080%, and V: 0.010 to 0.50%, limiting the Ti to less than 0.005%, satisfying equation; EC=2[C]−[Nb]/9−[V]/120.020, having an amount of precipitation of W contained in the steel material, in terms of analytical value obtained by quantitative analysis of potential electrolysis extraction residue by fluorescent X-ray analysis, of 0.0050% or less, and having 60% or more of its structural composition in a cross-section of the steel as a bainite structure.